The present invention relates to accurate measurement of urine temperature upon micturation as an indication of body temperature, and to the use of such measurements as an aid in natural methods of birth control.
Natural Family Planning is based on the recognition of physiologic signs and symptoms which identify the fertile and infertile phases of the menstrual cycle. More particularly, one known method of natural birth control is based on a recognition that basal (waking) body temperature (BBT) in fertile women is variable, and normally follows a cyclical pattern, shifting upwardly near the middle of each menstrual cycle. Within a few days of the occurrance of the upward shift in temperature, sufficient time has elapsed from the occurrence of ovulation, and a period of infertility begins, knowledge of which may be utilized in a program of natural birth control.
Basal body temperature is obtained by taking a temperature measurement at a standard time which ideally is just after waking and before rising. The traditional approach involves taking daily basal body temperature readings with a conventional thermometer, recording the daily measurements in graphical form, and interpreting the graph in order to identify the occurrence of a significant upward shift in temperature.
It will be appreciated that the traditional manual approach is somewhat unreliable for a number of reasons. For one, the accuracy of the temperature reading is sometimes poor. Additionally, it is frequently difficult for the average person to decide when the upward shift in temperature has occured. Another reason for unreliability is that it is inconvenient for most women to take their temperature every day immediately on waking, enter the temperature reading on a graph, and spend some time studying that graph. Taking shortcuts when doing these steps compromises the quality and meaning of the results.
In short, there necessarily are human errors involved in any method requiring very accurate reading of an instrument, correct entry of data on a chart and interpretation of temperature trends.
Accordingly, it has previously been proposed to automate the entire measurement and computation process in a portable device. For example, Lester U.S. Pat. No. 4,151,831 discloses various forms of a microprocessor-based instrument including a sensor for taking temperature readings, a digital clock for indicating when a temperature reading is to be taken, a memory for storing daily temperature readings, and a programmed microprocessor computing system for interpreting the results and indicating to the user when a period of infertility has begun. Lester proposes various forms of temperature sensor, including vaginal and oral temperature probes, and a skin temperature sensor.
Another example is disclosed in published U.K. patent application No. 80.40786, filed 19 Dec. 1980, and published as No. 2,066,528 on 8 July 1981, claiming the benefit of U.K. patent application No. 79.44063 filed 21 Dec. 1979, naming as inventors Wolff, Abrams, Royston and Humphrey, and entitled "Measurement of Basal Body Temperature". The Wolff et al device includes a probe for daily oral temperature readings. In order to reliably, and on a statistical basis, recognize the upward shift in BBT indicative of the beginning of a period of infertility, the device disclosed in the above-identified Wolff et al U.K. publication No. 2,066,528 implements a cumulative sum (CUSUM) algorithm described in the literature: J. P. Royston and R. M. Abrams, "An Objective Method for Detecting the Shift in Basal Body Temperature in Women", Biometrics, Vol. 36, No. 2, pp. 217-224 (June 1980).
A more recent example of a system implementing the Royston et al CUSUM algorithm for recognizing an upward shift in BBT is disclosed in U.S. Pat. Application Ser. No. 357,899, filed Mar. 15, 1982, by Andre E. Elias, and entitled "Microprocessor-Based Instrument for Detecting Shift in Basal Body Temperature in Women". The Elias instrument also includes a probe for daily oral temperature readings and includes a number of refinements relating to lower power consumption facilitating battery operation and to improved verification procedures for recognizing invalid temperature readings.
The entire disclosures of both the above-identified U.K. patent publication No. 2,066,528 and the above-identified U.S. application Ser. No. 357,899 are hereby expressly incorporated by reference herein for their descriptions of portable devices capable of recording daily temperature measurements and implementing a CUSUM test to recognize an upward shift in BBT.
Underlying the development of the Royston et al algorithm described in the above-identified literature reference, and implemented in the devices described in the U.K. patent publication No. 2,066,528 and in the U.S. application Ser. No. 357,899, is the fact that, even with accurate daily temperature measurements, many charts depicting basal body temperature throughout a menstrual cycle do not display a sharp, clear-cut rise. Various different patterns of basal body temperature rise are found, some of which are quite difficult to interpret without benefit of hindsight. The Royston et al article describes a statistical method for detecting an upward shift in basal body temperature, which method is based on the cumulative sum (CUSUM) test previously employed in the context of quality control of production processes.
For its detailed description of the CUSUM test for detecting upward shift in basal body temperature, the above-identified Royston et al article entitled "An Objective Method for Detecting the Shift in Basal Body Temperature in Women" is hereby expressly incorporated by reference. However, in order that the present invention may be better understood, the Royston et al algorithm is next briefly summarized.
The general problem is to begin with a plurality of sample values x.sub.1, x.sub.2 . . . x.sub.r, . . . x.sub.N of a random variable X. In the context of detecting an upward shift in BBT, each of the sample values x.sub.r is simply a daily temperature reading, appropriately corrected for time of day. It is then desired to detect an upward drift of the mean E(X) above some baseline B. As pointed out in Royston et al, in general, menstrual cycles in which ovulation has occurred show a biphasic BBT pattern, with a shift from a low post-menstrual level to a higher level around the time of ovulation. Ovulation usually takes place about two weeks before the onset of the next menstrual period. Royston et al refer to temperatures at the lower post-menstrual level to be "pre-ovulatory", and those at the premenstrual higher level as "post-ovulatory", although it is acknowledged that the temperature change does not actually prove that ovulation has occurred.
The baseline temperature is taken as a simple average of a number of daily readings. For example, the baseline may be taken as a simple average of eight daily readings, commencing on the fourth day following the beginning of a menstrual period. Thus, these eight days may be considered to be a baseline period. Temperature readings for the first three days of a menstrual period are not considered valid because they are sometimes still elevated as a carryover from the previous cycle.
The actual CUSUM test for the purpose of detecting an upward shift begins following the baseline period. The temperature reading for each day is generally compared to the baseline temperature (or, more accurately, to a reference temperature R derived from the baseline temperature). Positive deviations are represented by (x.sub.r -R). The cumulative sum (CUSUM) of positive deviations eventually becomes significantly large.
In the details of the implementation, a minimum change term is statistically predetermined, the minimum change term being related to the minimum basal body temperature rise considered to by physiologically significant as indicating a shift truly representative of ovulation. As reported by Royston et al, this minimum BBT rise is approximately 0.2.degree. C. and, for purposes of the CUSUM test, the predetermined minimum change term is 0.1.degree. C.
For purposes of comparison during the CUSUM test, rather than the actual baseline average temperature, a "central reference value" is employed, which is simply the actual baseline average temperature plus the predetermined minimum change term, which is 0.10.degree. C. This "central reference value" corresponds to the "reference temperature" R, introduced above.
The positive deviations (x.sub.r -R) are accumulated day by day, and their cumulative sum (CUSUM) compared to a decision interval, which is also statistically predetermined. By way of example the decision interval may be taken as 0.25.degree. C. On a day when the cumulative sum of positive deviations exceeds the decision interval, the CUSUM test is satisfied, indicating that a period of infertility has commenced, and the user may stop taking daily temperatures until the start of the next menstrual period.
The present invention further improves the instruments summarized above through the selection of a particular temperature measurement "site", namely measurement of the temperature of freshly-voided urine. Moreover, the present invention provides improved devices for rapid, convenient, accurate and reliable measurement of urine temperature for any purpose.
Axillary, rectal, vaginal and oral temperature measurements have all shown the mid-cycle upward shift in waking temperature, but all of these common sites have disadvantages. The axilla is not reliable if women have had the axilla exposed prior to temperature recording. Caution is advised when inserting the thermometer in the vagina; there are reports of accidental insertion in the urethra and transport to the bladder. The rectum is most often recommended, yet many women find this site unacceptable. Oral sites are more acceptable but perhaps not as reliable. Additionally, the time required to prepare the thermometer, to insert and leave in place, to read and finally to enter the data on a chart is so long that all but the most diligent and motivated women become disinterested in the method.
It has previously been recognized that urine temperature is a reliable indicator of body temperature. For example, the comparative value of temperatures of the mouth, rectum, urine, axilla and groin were observed by Burton-Fanning et al as early as 1903. (See Burton-Fanning, F.W. and Champion, S.C., "The comparative value of the mouth, the rectum, the urine, the axilla, and the groin for the observation of the temperature; Especially in regard to tuberculosis and to the effects of exercise and other conditions", The Lancet, 1903, Vol. 1, pp. 856-862.) These researchers employed the simple method of having male subjects void two to five ounces directly over the bulb of a mercury thermometer. The researchers reported correct readings in a majority of cases when temperatures were compared to rectal temperatures.
More recent experiments have employed insulated containers. For example, experiments by Ellenbogen et al (1972) and Murray et al (1977) utilized an insulated cup to obtain and record urine temperature with a mercury thermometer in an attempt to diagnose factitious fever. Both studies revealed a highly significant correlation with rectal temperatures as well as with oral temperatures. (See Ellenbogen, C., and Nord, B. "Freshly voided urine temperature: A test for factitial fever", Journal of the American Medical Association, Vol. 219, No. 7, p. 912 (1972); and Murray, H., Tuason, C., Guerrero, T., Claudio, M., Alling, D., and Sheagren, J. "Urinary temperature -- A clue to early diagnosis of factitious fever", The New England Journal of Medicine, Vol. 296, No. 1, pp. 23-24, (1977).)
As another example, a comparison of oral and urine temperature in adult male cardiac patients was performed by Sankey as reported in 1978. An electronic thermometer probe was used and placed in a styrofoam cup prior to the initiation of micturition. Temperature measurements were recorded at one, two, four and eight minutes after the completion of voiding. Voided urine temperature at one minute was found to be 0.81 degrees Fahrenheit higher than oral temperatures, and rapid cooling then proceeded (See Sankey, E. T. P. "A comparison of oral temperature readings and freshly voided urinary specimen temperature determinations," Masters Thesis, University of Delaware, 1978.)
Of somewhat greater pertinancy in the particular context of the present invention is a urine temperature measurement bottle devised by Fox et al for use in diagnosing hypothermia in the elderly. (See Fox, R. H., Fry, A. J., Woodward, P., Collins, J. C. and MacDonald, I. C. "Diagnosis of accidental hypothermia of the elderly", The Lancet, 1971, Vol. 1, pp. 424-427)
The Fox et al device comprises a one-liter plastic bottle fitted with a thin plastic funnel insert supplying a small overflow reservoir. Urine is funneled over a standard clinical thermometer, with the reservoir ensuring that the tip of the thermometer remains immersed with low rates of urine flow. Twelve male subjects tested the device, and the authors reported consistent correlations between rectal and urine temperature for urine volumes between 50 ml and 100 ml. A female version of the device which could be fixed in position on the toilet was mentioned, but test results using the female device version were not presented.